In dye transfer thermal printing, heat applied to a dye coated donor web member transfers the dye to a receiver material such as paper. The heat may be supplied by a source comprising a row of closely spaced resistive heat elements or a scanning light beam such as a laser. Image information signals determine the quantity of heat provided by the source at each pixel of the image. The amount of dye transferred from the donor member to the image pixel of the receiver is directly related to the quantity of heat supplied to the donor member. By varying the heat to the donor member, the image pixel receives more or less dye whereby the pixel density may be made to correspond to the image information signal. For monochrome images, each pixel is formed by a black dye. For color images, each pixel may comprise varying amounts of cyan, magenta and yellow dyes or varying amounts of blue, green and red dyes. U.S. Pat. No. 4,804,975 (issued to K. Yip on Feb. 14, 1989) discloses a thermal dye transfer arrangement that illustrates dye transfer utilizing a modulated laser diode.
Color dye transfer printing may involve mosaic or extremely narrow stripes of different colors which are selectively heated. U.S. Pat. No. 4,812,354 (issued to Takeo Sugiyama et al. on Mar. 14, 1989), for example, discloses a color image recording material in which hot melt inks are arranged in a mosaic or in stripes of widths in the order of 100 microns. The mosaic is exposed to develop a color image and the image is transferred to a receiver material. The preparation of the mosaic or stripe pattern, however, is relatively complex and color processing involves an exposure step followed by a printing step.
U.S. Pat. No. 4,764,444 (issued to Michael J. Simons et al. on Aug. 16, 1988) discloses a transfer element with a mosaic pattern of heat transferable dyes in which there is selective exposure of imaging layers after determining the location of the dye pattern to register the correct color components of the pattern. The registration is accomplished by a scanning laser or by orientation of the mosaic pattern with fixed positions such as perforations.
An alternative dye transfer arrangement involves passing the separate color donor material and one common receiver material through a scanning system once for each color. The thermal printing is repeated for the three or four separate colors that are used. As a result, the dye transfer process is relatively slow and suffers from color registration difficulties. A single scan is more efficient but provisions must be made for color registration. U.S. Pat. No. 4,710,781 (issued to Stanley W. Stephenson on Dec. 1, 1987) discloses a thermal printer color dye frame identification arrangement in which red and yellow light sources pass through a carrier having a repeated series of spaced frames of yellow, magenta and cyan colored heat transferable dyes onto detectors to identify the dye frames of the repeating dye frame series in a thermal printer. Such arrangements improve color registration, but require multiple donor passes.
The aforementioned color printing techniques require multiple step processes which increase the time required for printing. U.S. Pat. No. 4,626,868 (issued to Irving R. Tsai on Dec. 2, 1986) discloses a single pass printing arrangement in which a uniform toner mixture responds to a laser of particular wavelength to transfer a selected toner of the mixture to the printing surface. This single pass system, however, requires a uniform toner mixture and a relatively complex multi-wavelength laser system.
It is desirable to provide high speed single pass printing with simpler light and dye transfer arrangements than are known to be in use.